1. Field of the Invention
This invention relates to a fuel transfer system for a nuclear reactor and, more particularly, to a remotely operable fuel transfer system for transporting nuclear fuel assemblies between containment for a nuclear reactor and the fuel storage and handling building, when performing fuel loading or unloading operations.
2. Description of the Prior Art
As is well known in the prior art, nuclear reactor systems require periodic refueling, including particularly the exchange of fuel assemblies between the reactor and a fuel storage and handling building, both for removing spent fuel from the reactor and transporting same to the storage and handling building for subsequent inspection, reuse or disposal, and for supplying fresh fuel assemblies from the storage and handling building to the reactor. These fuel exchange operations are performed remotely under controlled conditions requiring adequate isolation of the reactor and its associated containment structure and the fuel storage and handling building.
FIG. 1 illustrates in simplified, schematic form, a typical nuclear reactor power system including a nuclear reactor vessel 10 supported within a containment structure 12. Typically, the walls of the containment structure are formed of reinforced concrete with suitable shielding. The top enclosure 11 of the reactor vessel 10 is capable of being opened through suitable remote means, to expose the interior of the reactor vessel 10 and particularly the fuel assemblies therein. A refueling machine 14 is mounted to travel on a suitable track 16 and includes a mast 18 which is capable of being positioned to extend into the interior of the reactor vessel 10, either to position a new fuel assembly therein or to remove a spent fuel assembly therefrom, and correspondingly to transport new fuel from, or transport spent fuel to, a fuel exchange location 20 within the containment structure 12. A fuel storage and handling building 22 serves both as a storage and handling facility for fresh fuel and a repository for receiving spent fuel. The fuel assemblies being exchanged are transported within the building 22 by a fuel handling machine 24 having a special tooling 26 for grasping the fuel assembly undergoing the exchange operation. The fuel assemblies, whether fresh or spent, are stored in appropriate locations within what is typically termed a fuel pit 28, schematically indicated to be included within the fuel storage and handling building 22 and separated from the exchange location 23 by a partition 29, access therebetween being afforded by a passageway 29a in the partition 29.
A transfer tube 30 connects the containment structure 12 and the fuel storage and handling building 22, extending from a position within the fuel exchange location 20 of the containment structure 12 to a position within a fuel exchange location 23 of the fuel storage and handling building 22. Openings 31 and 32 at the ends of the transfer tube 30 are closed during reactor operation and are open during fuel exchange operations to permit passage of fuel through the transfer tube 30. During the fuel exchange operations, boron-charged water is filled to a standing level, or head, of from 30 to 40 feet in both the containment structure 12 and the fuel storage and handling building 22, to control radiation levels and to protect workmen who are involved in the fuel exchange operations from exposure to such radiation.
The path through which the fuel assemblies are moved during such refueling, or fuel exchange operations, is known in the art variously as a refueling, or transfer, canal. Typically, a transfer car is mounted on suitable tracks so as to travel the length of the refueling canal, the car thus passing through the transfer tube 30 and extending, as far as is necessary, into the fuel exchange locations 20 and 23. Typically, the transfer car carries a fuel container which is pivotally mounted so as to be upended to a vertical orientation while within the exchange locations 20 and 23 and then to be disposed horizontally for passage through the transfer tube 30.
The conventional design of nuclear systems, and particularly the provision of the containment structure 12 and the separate fuel storage and handling building 22, interconnected by transfer tube 30, presents various problems in designing an effective transfer system. For example, the transfer system necessarily must be interrupted at the ends of the transfer tube 30 to accommodate closure of the valves 31 and 32, as is required for normal operation of the reactor. A further problem in the design of such transfer systems is the desire to keep as much equipment out of the containment structure 12 as possible and, particularly, to avoid the use of drive mechanisms in both the containment structure 12 and the fuel storage and handling building 22; preferably, a transfer system should employ only a single drive mechanism, located in the fuel storage and handling building 22. Accordingly, most transfer systems in use today utilize a long pusher arm which extends from a single drive system positioned in the fuel storage and handling building 22 and which engages the transfer car, so as to advance same through the transfer tube 30 and into the fuel exchange location 20, at which the fuel container is upended, as before noted. The use of the elongated pusher arm, however, undesirably extends the length of the refueling canal within the fuel storage and handling building 22, so as to accommodate both the pusher arm and the length of the transfer car when retracted into the fuel storage and handling building 22 -- sufficiently, moreover, to permit closure of the valve 32. The extension of the refueling canal within the fuel storage and handling building 22 not only increases the cost of the structure itself but as well imposes the requirement for storing a larger quantity of boron-charged water, introducing yet further expense.
Accordingly, prior art transport mechanisms have not been altogether satisfactory and thus there has been a continuing need for a more efficient and compact fuel transfer system.